The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the present disclosure.
In wireless systems, such as those operating under the IEEE 802.11 standard (including its different variants), an access point and the stations it serves make up a “basic service set” or BSS. When two nodes within a basic service set (e.g., two of the stations in the BSS) want to communicate, their signals include a duration field that specifies a transmit opportunity period (TXOP) during which other nodes within the basic service set should stay off the channel or operate at reduced power, to prevent collisions. For example, the stations may exchange a pair of signal frames called Ready-to-Send (RTS) and Clear-to-Send (CTS), which may include a field that specifies that. If another node detects activity on a channel and decides to share the medium with the detected activity, the node will remain idle for a duration known as a “backoff” period before trying again to use the medium, and after the backoff period, the node will operate at reduced power until the end of a “power restriction period” that is defined by the sum of the backoff period and one transmit opportunity (TXOP) period.
If a first node is in the same BSS as other nodes that have issued a signal that specifies a duration during which additional nodes should stay off the channel or operate at reduced power, then the first node must stay off the channel until the end of the duration. However, there may be multiple access points whose basic service sets overlap. In such an overlapping basic service sets (OBSS) situation, a first node that is in a different BSS than the other nodes may attempt to use a channel, detect that the channel is in use by the other nodes, and observe the backoff period and the power restriction period. However, because the first node belongs to a different BSS than the other nodes, the first node may not have retained the duration information broadcast by the other nodes. In such a case, after the power restriction period, if the channel is still in use by the other nodes, the first node will observe another backoff period and then resume full power operation, potentially causing a collision with the other nodes.